Exam 10: Distributions and Associations
When presenting a frequency distribution of a variable in a sample, why is it important to show percentage of cases for each value of the variable?
B
The mean and median value of a continuous variable are 10.4 and 9.5 respectively. The maximum value of the variable is 41.7. How would these values be shown in a box-and-whiskers plot?
A box-and-whiskers plot, also known as a box plot, is a graphical representation of a dataset that shows its central tendency and dispersion. The plot consists of a box and two "whiskers" that extend to the highest and lowest values within a certain range. Here's how the given values would be represented in a box-and-whiskers plot:
1. Median (9.5): This value is represented by a line inside the box and indicates the middle value of the dataset when it is ordered from lowest to highest.
2. Mean (10.4): The mean is not typically shown on a box plot because the plot focuses on medians and quartiles. However, if you wanted to include it, you could represent the mean with a different symbol or color on the plot, such as a small cross or dot.
3. Maximum value (41.7): This value is represented by the end of the upper whisker. However, in box plots, the whiskers typically extend to the last data point within 1.5 times the interquartile range (IQR) from the upper and lower quartiles. Any data point beyond this range is considered an outlier and is often represented with a separate marker such as a dot or asterisk. Since we don't have information about outliers or the IQR, we'll assume for this explanation that 41.7 is within the range and is the end of the upper whisker.
4. Minimum value: This value is not provided, but it would be represented by the end of the lower whisker. Similar to the upper whisker, the lower whisker extends to the minimum value within 1.5 times the IQR from the lower quartile, unless there are outliers.
5. Quartiles: The box plot is divided into quartiles, which are not provided in your question. The bottom of the box represents the first quartile (Q1), and the top of the box represents the third quartile (Q3). The space between Q1 and Q3 is the IQR. Without this information, we cannot accurately draw the box.
Given the incomplete information, a simplified version of the box-and-whiskers plot would show a box with a line at the median (9.5), a whisker extending to the maximum value (41.7), and potentially a marker for the mean (10.4). The minimum value and the quartiles are unknown, so they cannot be represented without additional data.
An ordinal variable called AGE GROUP contains five possible classes starting from "18-25" years, and a maximum class of "60-70" years. In addition to a frequency distribution, which measure of central tendency could be shown in presenting exploratory analysis results of the variable?
A
When would you use ANOVA, rather than a difference in means, to measure association between a continuous and a categorical variable? Explain with an example.
What is the difference between ANOVA and a 2-way ANOVA. Illustrate with an example.
Shape refers to how much values of a variable differ from one another.
Which is the best way to portray the distribution of a categorical variable? Explain with an example.
Discuss the plausibility of values, and their limits, for the numbers you present in your reports in question 1 and 2. Explain your reasoning.
A distribution with two modal values is called a multimodal distribution.
How would you define the term "outlier"? Choose the best answer
The mean and standard deviation of a distribution is 32.8 and 7.5, respectively. What is the z score of the number 70.6 in this distribution?
Median is the 50th percentile value of a variable whose values have been sorted from lowest to highest value.
The variance measure of a variable, with values clustered more closely around the mean value, is larger than when the values are more widely dispersed from the mean.
99.7% of values fall within +/- 3 standard deviation from the mean of a normally distributed variable.
A 2-way ANOVA measure is used to identify association between which type of variables?
The correlation coefficient between a dependent and an independent variable is -0.4. What can we say about association between the two variables?
What does the term "composition" refer to? Choose the best answer.
With the help of an example, illustrate the best way to present data distribution of a nominal variable. Explain your reasons for such a presentation.
What are the plausible limits to values of coefficient of determination?
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